@Dave: Do you still see the message on mobile? Now that the spam flag has been invalidated, it shouldn't show up at all. I think the difference is that the notice is a lot bigger relative to the rest of the page on mobile. (To be honest, I've never seen the notice at all, so it might not exist on the full page.)

@Mokubai: We talked about that internally and this is our main concern. We're going to look into it further, but I don't think most actual spammers would hit on this strategy. Also: xkcd.com/810

See also: Include an explanation of migrated questions in the Help Center.